Other online ad networks on the list included Pasadena, Calif.-based Openx, ranked No. 1, and San Francisco-based Quantcast, ranked seventh.

The list of infringing websites was compiled from the Google Transparency Report of domain names with the most Digital Millennium Copyright Act takedown requests. Top peer-to-peer offenders (mostly of music content) include BitTorrent.am, FileStube.com, Torrentz.com and FileTram.com.

The Annenberg report found that mainstream advertising financed 86% of the P2P search sites that feature illegally distributed content. It believes that many major brands are not aware that they are in fact the key source of funds for the piracy industry.

“Large pirate sites distribute illegal content and continue to steal trademarked, copyrighted content and siphon millions of dollars away from the creative community, making it much harder for artists to make a living,” Jonathan Taplin, director of the USC Annenberg Innovation Lab, said in a statement. “We do not believe that government regulation alone is the answer to the piracy problem, but rather that the self-regulation of major sectors like the online advertising industry could make it harder for the ‘Kim Dotcom’s’ of the world to unfairly exploit artists.”

Google said the report is mistaken in attributing that its ads represent a significant source of funding for piracy websites.

“Over the past several years we’ve taken a leadership role in this fight,” a Google spokesperson told the Los Angeles Times. “The complexity of online advertising has led some to conclude, incorrectly, that the mere presence of any Google code on a site means financial support from Google.”

Regardless, Tapin said the goal of the report to aid in helping these brands steer their ad dollars away from sites that exploit film, TV and music artists for what appears to be criminal gain.

“We look forward to working with advertising agencies and networks in the coming months to address this issue,” he said.